Evaluation of Tuberculin Skin Test Positivity and Early Tuberculin Conversion among Medical Intern Trainees in Tunisia

Background: As healthcare workers (HCWs), medical trainees are at a high-risk for acquisition of tuberculosis (TB) infection and disease. To our knowledge, there are no published data about TB infection among medical trainees in Tunisia. To determine the tuberculin skin test (TST) positivity and tuberculin conversion among a group of medical trainees in different departments at our institution. Materials and Methods: We performed a prospective study using the TST. The study was conducted in two steps: 1) an initial TST survey and 2) an evaluation of the TST conversion rates. Results: Among 114 participants, the TST was positive (≥10 mm) in 26.3% and negative (<5 mm) in 57%. The conversion rate of TST was 4%, which was only observed among the trainees assigned to the pulmonary departments. The significant predictor variables of TST positivity were a history of nosocomial TB exposure and training in a high-risk area. Conclusion: Despite the small number of participants, the high TB conversion rate among the trainees is alarming. This population represents an important target group for a latent tuberculosis infection screening program in countries with limited resources such as Tunisia.


Active tuberculosis (TB) infection in healthcare settings
is recognized as an important occupational risk for HCWs (1)(2)(3). The infection control measures recommended in the guidelines of the Centers for Disease Control and Prevention (CDC) are effective in reducing nosocomial Mycobacterium tuberculosis transmission (4)(5)(6). In highincome countries, these guidelines have been successfully implemented in healthcare settings, but in most lowincome countries, these control measures are insufficient.
Despite the resurgence of interest in occupational latent tuberculosis infection (LTBI) and TB during the past decade, relatively few recent studies have been published, and most of these studies did not report on the rate of TST conversion. Further, limited data are available regarding LTBI among newly employed HCWs, medical students, and interns (7,8). Moreover, there are currently no proper preventive measures for LTBI (9,10).
In Tunisia, the incidence of TB has been estimated at 32/100,000 population (11), and testing for LTBI is not Thus, we performed a prospective study using TST to determine the TST positivity and tuberculin conversion among a group of medical intern trainees in different departments of the medical training hospitals of Tunis.

Population and study design
A prospective survey using demographic and clinical data was performed. After 5 years of medical studies, medical students attend 2 years of an internship, bestowing the status of "internal trainees" or "interns," and rotate between the various medical, laboratory, and surgical departments for 4 months each. A list of interns attending different wards during the study was provided to us by the director of studies and training. During the study period (July 1-October 31, 2014), 250 interns, who were attending at the three main physician training hospitals of Tunis, participated as volunteers in the study.
Only 124 of the trainees had contact with patients, and they had been referred to participate in the study by a pulmonologist.
The internal trainees who had a history of TB, received immunosuppressive therapy, or been absent at the beginning of the survey were not included. The eligible interns were informed about the details of the study and signed a written consent form before participating in the study.
The study was conducted in two steps: in the first step, the TSTs were performed, and in the second step, TST conversions were identified. Each participant answered a standardized questionnaire developed by the study team at the beginning of the internship term. Then, a first TST (TST1) was performed. Students with TST1 <15 mm were   (12).

Screening for TB and LTBI
All participants were asked about TB symptoms and TB history.
The following participants were referred for assessment to a pulmonologist: -Participants with TST conversion and TST1 or TST2 Therapy for TB was administrated to participants who developed TB.
Then, if active TB was excluded, and if appropriate, therapy for LTBI, in accordance with current guidelines, was recommended for TST-conversion cases (12).

Ethics
The study was approved by the local ethics committee of Rabta teaching hospital. Eligible subjects were informed by the investigator about the rationale and aims of the survey. All participants provided written consent, and their personal information was protected.

Statistical analysis
We used Excel 2007 to enter all the information collected through the questionnaire and the TST results.
Then, data were analyzed using STATA software (version  Table 1.

Results of TST1
The rate of TST1 positivity was 26.3% and TST1 negativity was 57%; TST1 was ≥15 mm in 10% of samples.
No difference was found between age and sex (p >0.05).
The TST results according to the previous training in highrisk areas and clinical level of training are summarized in Table 2.  Table 3).